"Multi-axis motion control systems are used extensively in manufacturing and laboratory research for positioning purposes," said a CAS DataLogger spokesperson. "These systems often rely on feedback from position sensors to maintain closed-loop control for improved accuracy. In test and measurement applications, it is often desirable to use additional inputs as part of the feedback loop."
For example, in scanning tunneling microscopes, a sample is moved in the X- and Y-axis while a feedback loop drives an actuator to maintain a constant tunneling current between a probe and sample in the Z-axis. The output of this loop can be used to generate a topographic, or height profile of the sample. "To achieve the necessary control and accuracy, ADwin data acquisition and control systems are ideal for use in these applications," said the spokesperson. "The ADwin-which incorporates digital and analog inputs and outputs with a real-time processor in a single unit-can drive stepper motors and/or other actuators, using feedback from various position sensors or other voltage or current inputs."
A system based on an ADwin-Gold real-time system, in this case, designed to test the trigger switches of variable-speed power tools, features six stations that allow up to six separate switches in parallel to be tested. Each test station has a stepper motor that drives an actuator to simulate a person pressing the switch. A home sensor and encoder provide information on the position of the switch. The ADwin system, in addition to driving the stepper motor and reading the position information, measures the RMS voltage, RMS current and duty cycle (in the case of PWM control) of the output from the switches.
The ADwin's multitasking capabilities provide independent control of each station. One main, high-priority task implements the main control loop for all six test stations. This control loop includes functions that:
- Find the home position
- Drive the actuators
- Move the switch to a specified position
- Monitor the voltage, current and other input parameters.
Practical Example
A main loop executes at 10 kHz, which allows accurate measurement of the switch parameters. The move function implements a trapezoidal velocity profile-an algorithm determines the distance from the current position to the target position and calculates a velocity profile with a given acceleration, target velocity and deceleration.
Each test station has an individual process associated with it that sequences through the test steps to verify the operation of the switch. These separate processes allow for independent control of each station so that if the switch at Test Station One fails, it will have no impact on the test operation of a switch on Test Station Two. These processes run at 100 Hz, which is more than fast enough since the RMS data is updated at a line cycle frequency of 60 Hz. A user interface designed with LabView controls and monitors the operation of each test station through the use of global data that is automatically synchronized between the ADwin hardware and a PC.
"This ADwin-based control system meets or exceeds all of the original design goals, performing substantially better than previous devices that utilized PC-based data acquisition boards to perform the measurement and control functions," said the spokesperson. "The previous solution required a PC and DAQ hardware for each test station, at a significantly higher cost to test switches in parallel."
This solution also highlights some of the most notable features of ADwin systems, including:
- Support for multiple concurrent processes
- Tightly-coupled analog and digital I/O
- Fast real-time operation
- Deterministic operation.
These capabilities can be useful in a number of other positioning applications, including:
- Dynamic test stands for vibration, force or stress
- Marking or engraving systems
- Automated assembly equipment
- High-speed positioning equipment.
For more information contact:
CAS DataLoggers
8437 Mayfield Rd., Unit 104
Chesterland, OH 44026
800-956-4437 / 440-729-2570
sales@dataloggerinc.com
www.dataloggerinc.com